Acoustic wave touch position sensors are known to include a touch substrate having a group of transmitters positioned along a first edge of the substrate for generating Rayleigh waves that propagate through the substrate in an X direction to a group of detectors positioned on a second edge of the substrate opposite to the first edge. A group of transmitters is also positioned along a third edge of the panel for generating Rayleigh waves that propagate through the substrate in a Y direction to a group of detectors positioned on a fourth edge of the substrate opposite to the third edge. Interruption of intersecting waves by touching the panel causes output signals to be developed at an X detector and a Y detector defining the point of intersection. Acoustic touch position sensors are also known wherein only two transducers per axis are required. For each axis, one transducer imparts either a Surface Acoustic Wave or a Shear wave that propagates along the perpendicular axis on which a first reflective grating is disposed to reflect portions of the acoustic wave along plural parallel paths of differing lengths to a second reflective grating. The second reflective grating reflects the surface acoustic wave to a second transducer where the signals are received for processing. The reflective gratings associated with the X-axis are perpendicular to the reflective gratings associated with the Y-axis so as to provide a grid pattern to enable coordinates of a touch on the substrate to be determined. For acoustic touch position sensors that utilize an acoustic wave that can be reflected off an edge of the substrate, for example a Shear wave, the second reflective grating and second transducer may be eliminated. In such a sensor, one transducer imparts the acoustic wave for propagation along the first grating which reflects the acoustic wave along plural parallel paths to a reflective edge of the substrate. The reflective edge of the substrate reflects the acoustic waves back along the plural parallel paths to the first grating which in turn reflects the acoustic waves back to the one transducer for processing.
Although the above-described types of touch panels adequately detect a finger touch on the touch surface of the substrate, they are not responsive to a touch by a non-active stylus of a general type, such as a pen or pencil, having a small, well-defined point of contact with the touch substrate. Acoustic wave touch panels for use with a stylus are known; however, the known panels require a specific type of active stylus. Such active styli typically include a transducer to generate an acoustic wave that is transmitted into the acoustic wave touch substrate wherein the stylus is tethered to the control circuitry of the touch panel. These touch panels typically require complex circuitry and processing to detect a touch on the touch panel by the active stylus.